Methods and Arrangements for Estimating Uplink Coverage in Wireless Communication Networks with Dynamic Cell Coverage

ABSTRACT

The present invention relates to methods and arrangements in cellular communication networks exhibiting dynamic cell coverage, in particular, to estimate the uplink coverage in a network in operation. According to the method of the present invention a received rate is determined from at least one mobile terminal being in a communication session, by measuring the number of received transport blocks during a predetermined time interval. The received rate is compared with a predetermined expected rate, and if the received rate is below the expected rate poor coverage is identified. Since the coverage is potentially load dependent an estimate of the uplink coverage has been obtained.

FIELD OF THE INVENTION

The present invention relates to methods and arrangements in cellularcommunication networks exhibiting dynamic cell coverage. In particularthe invention relates to a method and arrangement to estimate the uplinkcoverage in a network in operation.

BACKGROUND

Careful planning of the wireless cellular communication networks hasbeen of high importance ever since the development of the early analognetworks such as NMT and AMPS. A careful planning is equally importantfor today's cellular systems such as the WCDMA based UMTS and CDMA-2000,and will be as important in future systems.

As is well known, the often depicted hexagonal pattern of the basestations of a wireless network is a simplification. In reality, with forexample a varying topography or a plurality of man-made obstacles suchas tall houses, the demand for coverage almost everywhere, includingindoors and underground etc, the planning of a network is far fromtrivial. In addition to the mentioned factors relating to the radiopropagation properties a successful network planning must take intoaccount the varying demands on capacity. In certain portions of thenetwork, corresponding to densely populated areas, for example, thecapacity must by higher than in more rural areas. This capacity need mayshift during a day. During working hours the demand for capacity willtypically be highest in for example office areas, while in the eveningsand nights the demands will be very low.

The coverage area of a wireless network is defined as the area whereinthe users have access to their subscribed services. It is vital both tothe users and the operators of wireless network that the wireless systemhas adequate coverage.

In principle, improving coverage is simple, it is only a matter ofdeploying a sufficiently dense pattern of base stations. However, sincethe cost of a cellular system is to a very high degree proportional tothe number of base stations, an operator tries to avoidover-dimensioning. The cost of a base station comes both from theequipment itself and its installation cost, but also to a high degreeoperation and maintenance costs and the cost for renting properties forthe base stations. In addition environmental and esthetical issues havebeen raised concerning base station mast and antennas. Hence, operatorsstrive to fulfil the coverage requirement using as few base stations aspossible.

A vast number of methods and tools have been developed and deployed toestimate coverage. Three main approaches, which often are used incombination, in assessing the coverage of a network may bedistinguished: propagation predictions; drive tests and trafficstatistics.

Propagation predictions rely on very accurate map data, both withregards to the natural topography and to man made objects. This is anobvious starting point the planning a network, but can, although greatimprovements have been reported over the years, only give rough coveragepredictions. This is particularly true for indoor environments.

Drive tests, which comprise of measuring the radio coverage in thefield, typically by vehicle-based measuring units, give reliable datafor the location of the measurement. However, to cover all parts of anetwork with a drive test is in practice impossible—the tests aretypically confined to roads and the like. In addition, drive tests aretime-consuming and expensive.

Traffic statistics are performed on a running network. Most commonlydropped calls are identified and related to a geographical area.However, the methods can not discern what caused the dropped call, andsince there are many reasons for a dropped call apart from bad coverage,the dropped call statistics are a blunt instrument for cell planningpurposes. In addition, a bad coverage does in certain network notnecessarily, or immediately, lead to a dropped call, but degradedperformance. Dropped call statistics does not account for these cases.

In practice the cell planning often involves all three approaches, thepropagation predictions is performed as a first measure to plan thenetwork; drive tests and traffic statistics are used in a later state toassess coverage of the existing network.

Cell planning has become even more complicated with the widespread useof CDMA-based access technology, such as WCDMA. CDMA systems will, dueto interference-limited nature, exhibit dynamic cell coverage, i.e. thecoverage of a cell will be dependent on the load in the cell. Thisbehaviour, intrinsic to CDMA, is commonly referred to as cell breathing.Cell breathing can be accounted for in propagation predictions used forcell planning. EP 1,294,208 and U.S. Pat. No. 5,710,758 teach methods ofimproving commonly used simulation approaches in cell planning byincorporating the effects of cell breathing. The disclosed methods takecell breathing into account but have the drawback in common with thepreviously mentioned prediction methods that they for a real network,only give rough estimates of the real radio environment. Hence, methodsand arrangement for improving the cell planning and/or uplink loadcontrol, based on traffic statistics and which handles the dynamic cellcoverage is needed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide methods and arrangementthat facilitate an improved cell planning and/or improved uplink loadcontrol in cellular communication networks exhibiting dynamic cellcoverage. In particular, an object of the present invention is toprovide reliable traffic statistics in an up and running network.

The above stated object is achieved by means of a method according toclaim 1, a method in a radio network controller (RNC) according to claim8, a radio network controller according to claim 12, and a systemaccording to claim 14.

The present invention provides a method for estimating uplink coveragein a wireless communication system, which the exhibits load dependentcell coverage. The method gathers traffic statistics related to radiocoverage in individual cells in a wireless communication system inoperation, and comprises the steps of:

-   -   determining a received rate from at least one mobile terminal        being in a communication session, by measuring the number of        received transport blocks during a predetermined time interval;        and    -   comparing the received rate with a predetermined expected rate,        and if the received rate is below the expected rate, identifying        poor coverage. Since the coverage is potentially load dependent        an estimate of the uplink coverage has been obtained.

Preferably, if the received rate is below the expected rate, anindication of insufficient coverage is stored for later analysis, eitherfor cell planning purposes or radio resource management purposes such asuplink load control. Alternatively, or in combination with storing theindications of insufficient coverage, the received rate is stored. Thispart of the method according to the invention is preferably performed ina radio network controller (RNC) node in the wireless communicationsystem.

According to a first aspect of the present invention the methodcomprises a further step of performing a cell planning function usingthe stored indications on insufficient coverage and/or the storedreceived rates to identify areas with poor radio coverage. This ispreferably performed in an O&M node which retrieves the gathered trafficstatistics from the RNC.

According to a second aspect of the invention the method comprises afurther step of performing a load control function on the storedinformation to identify inadequate admission control thresholds bycomparing the number of indications of insufficient coverage, or a ratioof transmissions giving rise to indications of insufficient coveragecompared to the total number of transmissions, with a predetermined loadvalue, said load control function performed per cell, and suggesting alowering of the admission control threshold if the load control functionhas identified an inadequate admission control threshold for the cell.The load control function is preferably performed in the RNC.

According to a third aspect of the method of present invention the stepof comparing comprises the substeps of:

-   -   comparing the received rate of a first TTI and the received rate        of a second consecutive TTI with the expected rate;    -   determining if the received rate of the second TTI is zero, and        storing an indication of insufficient coverage and/or the        received rate only if the received rate of both the first and        second TTI are below the expected rate and the rate of the        second TTI is nonzero, whereby discerning between low received        rate due an ending transmission and low received rate possibly        due to poor coverage. In the case of low received rate due to an        ending transmission the rate of first TTI may be below the        expected rate, but the rate of consecutive second TTI will in        that case be zero.

Thanks to the invention it is possible to estimate the uplink coveragefrom traffic statistics in an up and running network in a way that doesnot require control signalling over the air interface.

One advantage afforded by the present invention is that the method maybe used for an improved cell planning as it gives an estimate of theload dependency of the cell coverage for the cells in the wirelesssystem.

Yet another advantage afforded by the present invention is the ability,according to one embodiment, to discern between low received rate due anending transmission and low received rate possibly due to poor coverage.

A further advantage is that the method according to the invention can beutilized to improve the radio resource management procedure such asadmission control.

Further advantages and features of embodiments of the present inventionwill become apparent when reading the following detailed description inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a-c is a schematic illustration of cell breathing in a cellularnetwork in which the methods and arrangements according to the presentinvention may advantageously be applied;

FIG. 2 is a flowchart of the method according to the invention;

FIG. 3 is a schematic illustration of a system according to the presentinvention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like numbers refer to like elements.

Power control is an essential feature in all CDMA-based wirelesstechnologies, not at least in WCDMA. Power control is utilized in bothdownlink and uplink. The principles for the power control are fairlysimple, although the implementation is far from trivial, mainly due tothe speed the power control need to be performed with and the fact thatall changes in transmit power in principle effects all entities in acell. In a simplified power control scheme a transmitter sends itssignal with a certain transmit power. The receiver estimates the qualityof the received signal, and if the signal is poor the receiver requestthe sender to increase its transmit power. On the other hand, if thereceiver determines the signal as being unnecessarily strong, thereceiver request the transmitter to lower its transmitting power.

When a transmitter, either in a base station or a mobile terminal, usesits maximum transmit power, which may be the maximum allowed transmitpower—not necessarily the maximum in power capacity, it is of course notpossible to further increase the power as a response to power controldemands from the receiver. If the situation persists, it is probablethat it is impossible to maintain the communication quality. Eventually,the coverage is lost and the user will be dropped. This situation mayoccur both in uplink and downlink.

The aim of the cell planning is, as described in the background section,to provide coverage. However, coverage problems as described above willoccur in all networks, especially in newly implemented networks or ifchanges have been made to the network or to the radio environment whichthe network operates in. Preferably coverage problems should be detectedas early as possible in order to avoid severe problems. This is possiblein downlink, since the network, through the base station and RadioNetwork Controller (RNC), has access to accurate information about thebase station transmit power, which determines the downlink coverage. Ifthe system, even at low load, operates close to the maximum code power,i.e. the maximum transmit power that is allocated to any particularuser, it is a clear indication on inadequate coverage, and that it willbe difficult to guarantee the service quality at high load. Analysislike this is typically performed for cell planning purposes in aO&M-node, based on reports from the RNC.

In uplink, the above described downlink method is not feasible, sincethe network does not normally has knowledge of the transmit power usedby each individual mobile terminal. In principle, it would be possibleto order each mobile to include their used transmit power in measurementreports sent to the network. However, in practice it would not befeasible to report this quantity sufficiently often, since it wouldrequire a substantial control signaling over the air interface thatwould consume an unjustifiably large amount of the scarce radioresource.

A cause of unintended poor coverage in CDMA-based networks is the abovedescribed cell breathing. The effects causing the dynamic cell coverageare well understood, but it is very complex to exactly predict theeffect on the actual coverage in a real cellular network. In FIG. 1 a-ca cellular network is schematically illustrated. A plurality of basestations 105:1-5 serves their respective cells 110:1-5, defined by cellboundaries 115. The cell boundary between two adjacent cells 115:1,115:2 is typically defined as the location there the signal strengthfrom the two adjacent base stations 105:1 and 105:2 are equal. In FIG. 1a a situation is represented wherein the load is moderate in all cells.In FIG. 1 b the load has increased and in cells 110:1 and 110:4 to adegree that the coverage has been affected—the cell breathing has causedthe cells to shrink. In some cases this only leads to a movement of thecell boundary, as in the example between cells 110:1 vis-à-vis cells110:2 and 110:3. In other cases the shrinking of the cells may result inareas that has no coverage, as indicated by the dashed areas 120, incell 110:4.

In advanced CDMA-systems such as WCDMA a multitude of transmission ratesare handled by the system. A base station may for example provide hightransmission rate services in a small area and lower rate transmissionservices in a larger area. In FIG. 1 c the base stations provide hightransmission rate service all through the network, provided the load ismoderate. If the load is increased a situation occurs then certain basestations, illustrated by base stations 105:1 and 105:4 in cells 110:1and 110:4, respectively, can not provide the high transmission rate inall of their cells, although coverage is not completely lost in anypart. This can be seen as these cells having a plurality of cellboundaries corresponding to different data transmission rates. Thedashed inner circles 130:1 and 130:4 correspond to the “cell boundaries”of high transmission rate services while the outer boundaries 115:1 and115:4 of the cell remains unchanged. The outer boundaries now representthe cell boundaries of the lower transmission rate services. In thisscenario a “dropped call” due to poor coverage does not necessarilyimply that the connection is dropped completely, rather that the user isnot able to have access to the high transmission rate services that theuser subscribe to and possibly is guaranteed by the operator. The term“insufficient coverage” will in this application be used to indicatethat a user, due to poor coverage, is experiencing a lower transmissionrate than the user should expect. Insufficient coverage does notnecessarily lead to a dropped call.

The term “mobile terminal” should be interpreted as any user deviceutilizing the wireless communication system. Mobile terminals include,but are not limited to mobile phones, laptop and handheld computers withwireless communication facilities, cameras and other electronicequipment with wireless communication facilities. In addition, manyother devices and machines such as vehicles, stand-alone measuring andproduction units, vending machines, etc may advantageously be providedwith wireless communication facilities, and are for the purpose of thisapplication and with regards to the communication aspects to be regardedas mobile terminals.

According to the present invention the network, i.e. the RNC, determinesthe transmission rate from a mobile terminal by measuring the number ofreceived transport block during a predetermined time interval. From thismeasure a received rate is calculated. If the received rate is lowerthan an expected value this is identified as an indication ofinsufficient coverage and reported to a traffic statistic function. Themeasurement and identification is done per mobile terminal. By gatheringtraffic statistics over a period of time, and preferably for a pluralityof mobile terminals, areas or cells showing a high rate of insufficientcoverage can be identified. These areas represent areas with poorcoverage (for the intended services) and the operator may now takeappropriate actions to improve the coverage. The actions that may betaken are as such known in the area of cell planning, for example addingnew cells, adjusting/replacing antennas, adjusting admission thresholdetc.

The method and arrangement will now be exemplified in a radio accessnetwork according to UMTS, which should be regarded as a non-limitingexample. UMTS specific terms such as transport format (TF), transportformat combination limitation (TFC limitation), transmission timeinterval TTI, should be regarded as generic terms with, for the skilledperson, obvious counterparts in other radio access systems. Details ofthe mentioned formats and protocols are to be found in the UMTSspecifications 3GPP TS 25.321 and 3GPP TS 24.133.

In UMTS, the feature TFC limitation is used in the uplink. For eachuplink transmission, the mobile selects one transport format, TF, foreach transport channel. Each transport format is associated with atransmission rate. The higher the transmission rate, the more transmitpower is required. In general, the mobile terminal uses the highesttransport format, i.e. the transport format corresponding to the highesttransmission rate. However, in situations when the transmission powerapproaches the maximum, the mobile terminal starts using a lowertransport format. This is performed by sending fewer transport blocksduring a TTI. For example, with a 384 kbps bearer, it is possible totransmit up to 12 transport block during 10 ms, one TTI. With themaximum transport format, the mobile terminal transmits 12 transportblocks in the 10 ms interval, but with a lower transport format, fewertransport blocks are transmitted in the time interval. This will improvethe possibility of maintaining the connection, but at the cost of alower transmission rate. The mobile terminal informs the base station ofthe chosen TF, which is needed for the decoding, but according to thestandard TF is only used within the decoding and not reported anyfurther.

In the method according to the invention, described with reference tothe flowchart of FIG. 2, the procedure of the mobile terminal changingthe transport format to adjust to the coverage is utilized for gatheringtraffic statistics usable for cell planning. The method according to theinvention comprises the steps of:

205: A rate measuring function, preferably in the RNC, statisticgathering function measures, per mobile, the number of transport blocks,N_(tb), received during a TTI for at least one mobile terminal withwhich the networks is maintaining a communication session. The number oftransport blocks received divided with the length of the TTI correspondsto a received rate, R_(r)..

R_(r)∝N_(tb)/TTI

210: The rate measuring function compares the received rate, R_(r), orthe received rate from a plurality of TTI's, with an expected rate,E_(r).. If the received rate, R_(r)., is below the expected rate,E_(r)., it is possible that the user do experience insufficientcoverage, and the comparison may be further analyzed in the substeps of:210:1 If the received rate, R_(r), from at least two consecutive TTI'sare below the expected rate, E_(r)., it is a possible indication ofinsufficient coverage.210:2 If the received rate, R_(r), of a first TTI is below the expectedrate, E_(r)., and if the R_(r) of a second TTI, consecutive to the firstTTI, is zero, it is an indication of that the transmission from themobile terminal is ending/has ended. The reason for the low R_(r) of thefirst TTI is in this case that the mobile terminal does not have enoughtransport blocks to transmit, not insufficient coverage. Therefore, noindication of insufficient coverage should be reported. If the R_(r) ofthe second TTI is nonzero an indication of insufficient coverage isreported (step 215).215: If the comparison/analysis of step 210 determines insufficientcoverage, an indication of insufficient coverage is reported to andstored by a statistic gathering function, preferably also residing inthe RNC.220: The steps 205 to 215 are repeated throughout the communicationsession. Hence, a plurality of indications of insufficient coverage maybe reported for each mobile terminal and communication session.225: In a analyzing step, typically to be taken at regular intervals orif other indications of poor coverage, for examples complaints, havebeen received, the statistics of the indications of insufficientcoverage are analyzed. The analysis may be performed in various way, andmay include comparing the number of indications of insufficient coverageper cell with the total number of transmissions in that cell to identifycells with poor coverage. The analyzing step is typically performed in,or in connection with, a cell planning function in an O&M-node, whichhas received the gathered statistics.

The method according to the invention may be constantly activated in thewireless communication system. Alternatively the method is activated ondemand, for example after initialization of a new system (or part of asystem), after introduction of new base stations or antennas in anexisting systems, or if indications of lost services, such as complains,have been received.

The expected rate, E_(r), may be corresponding to the highest transportformat that should be available to the user in the network or in theparticular cell. Alternatively, the expected rate, corresponds to atransport format that the mobile terminal has reported to the network atcommunication set up as the preferred transport format for thecommunication session, or part of communication session.

The indication of insufficient coverage reported in step 215 indicatesthat the mobile terminal is not able to use the expected rate. Thereceived rate, R_(r), corresponds to the rate for which the mobileterminal actually has coverage. For example, if the mobile repeatedlychooses a transport format corresponding to a bitrate of 128 kbps themobile has 128 kbps coverage. This is utilized in a further embodimentof the invention in which steps 215 and 225 are modified according to:

215′: If the comparison/analysis of step 210 determines insufficientcoverage, the received rate, R_(r), and possibly also an indication ofinsufficient coverage is reported to and stored by a statistic gatheringfunction.225′: In the analyzing step of the statistics of the stored receivedrates, R_(r), is analyzed to give an estimate of the coverage to beexpected by for a specific transmission rate. The ratio of transmissionsthat exhibit the specific transmission rate is ascribed as the ratio ofthe cell that exhibit the specific transmission rate.

If, for example, the received rates indicate that only 2% of thetransmission that are allowed to use a 384 kbps bearer actually uses thehighest transport format, the analysis in step 225′ assumes that only 2%of the cell has coverage for 384 kbps. If desired, the operator may takeactions to increase the 384 kbps coverage in the cell.

This analysis can be extended to a plurality of transmission rates orintervals of transmission rates, by analyzing the ratio of transmissionsthat exhibit a received rate in a predetermined interval and ascribingthat ratio as the percentage of the cell that has coverage in thepredetermined interval.

Various kinds of statistical means of the received rate, {circumflexover (R)}_(r), may be used instead of, or in combination, with thereceived rate, R_(r),. For example the mean received rate for apredetermined number of consecutive TTIs. This could be useful inlimiting the fluctuations in reported received rates, and wherebyfacilitate further statistical analysis. However, care must be taken notto use a mean that conceals the effects of poor coverage. In addition,the use of a mean value should preferably not limit the abilities todiscern between low received rate due to the ending of a transmissionand low received rate due to insufficient coverage (step 210:1).

In a further embodiment of the invention the procedure of measuringreceived rate and comparing with an expected value is utilized for loadcontrol. Whereas the previously described embodiments of the inventionrelates to cell planning and is performed in a timescale of weeks ormonths, load control is constantly taking place in the system, and theactions suggested by this embodiment may be performed in the timescaleof an hour or a day.

As previously described, the coverage of a cell is reduced when the loadin the cell increases. The effects of the dynamic cell coverage can inbe mitigated by a procedure known as admission control. In cases withhigh load it is often preferred to rather block access of new users,than reducing the capacity or drop existing users. The admission controlthreshold defines the level of uplink load when the system should startblocking new users. On accepting a new access the admission controlmakes an estimate of how the new access will affect the total load inthe cell. If the total load is estimated to exceed the admission controlthreshold the new access is denied. A comprehensive description of theadmission control procedures is to be found in WCDMA for UMTS, ed. ByHarri Holma and Antti Toskola, John Wiley & sons Ltd 2004, pp 264-268.The admission control procedure requires reliable measures on the uplinkload. However, as described, such measures have not previously beenavailable.

According to this further embodiment of the invention the method iscomplemented with the step of:

221: A load control function in the RNC analysis the gather statisticsof indications of insufficient coverage. The analysis is typically perbase station, and comprises the substeps of:221:1 Compare the number of indications of insufficient coverage, or aratio of the number of transmissions giving rise to indications ofinsufficient coverage compared to the total number of transmissions, fora base station, with a predetermined value.221:2 If below the predetermined value the load control function hasidentified an inadequate admission control threshold, and suggests alowering of the admission control threshold.

The predetermined value is typically set by the operator of the network.It is preferably a rather small number (or ratio) in a well functioningnetwork, but non-zero, as poor transmission will always occur in somecases, for example due to faulty user equipment. Cases, which preferablynot, is made to effect the admission control threshold.

The changing of the admission control threshold can be automated orperformed by a network operator, who has received information of theneed of an action from the load control function. The load controlfunction is preferably performed in the order of once per day, or a fewtimes per day.

The use of the received rate to facilitate load control according tothis embodiment may be combined with the previous use for cell planning.Alternatively only the load control or cell planning is utilised. In thecase of only load control, the cell planning step (step 225, 225′) isomitted.

The setting of the admission control threshold affects the outcome ofthe cell planning function as described with reference to FIG. 2. A lowadmission control threshold will result in few users experiencinginsufficient coverage, but possibly too many blocked new accesses.Therefore, in evaluating the statistics of indications of insufficientcoverage the value of the admission control threshold is preferablytaken into account, especially if both the load control function and thecell planning function is activated in the same system.

The wireless communication system according to the present inventioncomprises a plurality of functional parts or modules, preferablyimplemented as software code means, to be adapted to effectuate themethod according to the invention. In FIG. 3 the main nodes whichcomprise the main functional modules, which are involved in the processof measuring and analysing the received rate, are schematicallydepicted. The terms “comprising” and “connected” should here beinterpreted as links between functional parts and not necessarilyphysical connections.

A mobile terminal 305 is engaged in a communication session via the basestation 310. The base station 310 delivers the decoded data to the RNC315, from which the RNC may determine the received rate in a ratemeasuring module 316. In a comparing module 317 the measured receivedrates are compared to the expected rate. The results from the comparisonmodule 317 are stored in the storing module 318 of the RNC 315. If thestatistics of indications of insufficient coverage are used for loadcontrol, the RNC comprises a load control module 319 in connection withthe storing module 318. For the purpose of cell planning the statisticgathering module 318 is accessible from an O&M node 320.

The method according to the invention giving a reliable estimate of theuplink coverage may be utilized in various ways, which has beenexemplified in the different embodiments of the invention. A reliableestimate of the uplink coverage could be useful also for other, presentor future, radio resource management and/or cell planning purposes, suchas providing information to the processes of inter-system orinter-frequency handovers.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

1. A method for estimating uplink coverage in a wireless communicationsystem, the wireless communication system possibly exhibiting loaddependent cell coverage, wherein the method gather traffic statisticsrelated to radio coverage in individual cells in a wirelesscommunication system in operation, characterised in that the methodcomprises the steps of: determining a received rate from at least onemobile terminal being in a communication session, by measuring thenumber of received transport blocks during a predetermined timeinterval; and comparing the received rate with a predetermined expectedrate, and if the received rate is below the expected rate, identifying apossible uplink load dependent effect on the cell coverage.
 2. Themethod according to claim 1, further comprising the step of: storing anindication of insufficient coverage if the received rate is below theexpected rate and/or storing the received rate if the received rate isbelow the expected rate.
 3. The method according to claim 2, furthercomprising the step of: performing a cell planning function using thestored indications on insufficient coverage and/or the stored receivedrates to identify areas with poor radio coverage.
 4. The methodaccording to claim 2, further comprising the steps of: performing a loadcontrol function on the stored information to identify inadequateadmission control thresholds by comparing the number of indications ofinsufficient coverage, or a ratio of transmission giving rise toindications of insufficient coverage compared to the total number oftransmissions, with a predetermined load value, said load controlfunction performed per cell; suggesting a lowering of the admissioncontrol threshold if the load control function has identified aninadequate admission control threshold for the cell.
 5. The methodaccording to claim 2, further comprising the steps of: performing a cellplanning function using the stored indications on insufficient coverageand/or the stored received rates to identify areas with poor radiocoverage; performing a load control function on the stored informationto identify inadequate admission control thresholds by comparing thenumber of indications of insufficient coverage, or a ratio oftransmission giving rise to indications of insufficient coveragecompared to the total number of transmissions, with a predetermined loadvalue, said load control function performed per cell; and suggesting alowering of the admission control threshold if the load control functionhas identified an inadequate admission control threshold for the cell.6. The method according to claim 2, wherein the step of comparingcomprises the substeps of: comparing the received rate of a first TTIand the received rate of a second consecutive TTI with the expectedrate; determining if the received rate of the second TTI is zero, andstoring an indication of insufficient coverage and/or the received rateonly if the received rate of both the first and second TTI are below theexpected rate and the rate of the second TTI is nonzero, wherebydiscerning between low received rate due an ending transmission and lowreceived rate possibly due to poor coverage.
 7. The method according toclaim 2, wherein in the comparing step the received rate is stored, andin the a cell planning function the stored received rates are analyzedto give an estimate of the coverage to be expected for a specifictransmission rate, by ascribing the ratio of the transmissions thatexhibit the specific transmission rate as the ratio of the cell thatexhibit the specific transmission rate.
 8. A method in a radio networkcontrolling node in a wireless communication system, the wirelesscommunication system possibly exhibiting load dependent cell coverage,wherein the method gather traffic statistics related to radio coveragein individual cells in a wireless communication system in operation,characterised in that the method comprises the steps of: determining areceived rate from at least one mobile terminal being in a communicationsession, by measuring the number of received transport blocks during apredetermined time interval; comparing the received rate with apredetermined expected rate, and if the received rate is below theexpected rate, identifying a possible uplink load dependent effect onthe cell coverage; and storing an indication of insufficient coverage ifthe received rate is below the expected rate and/or storing the receivedrate if the received rate is below the expected rate.
 9. The methodaccording to claim 8, wherein stored indications of insufficientcoverage from a plurality of transmissions are used for radio resourcemanagement.
 10. The method according to claim 9, further comprising thesteps of: performing a load control function on the stored informationto identify inadequate admission control thresholds by comparing thenumber of indications of insufficient coverage, or a ratio oftransmission giving rise to indications of insufficient coveragecompared to the total number of transmissions, with a predetermined loadvalue, said load control function performed per cell; and suggesting alowering of the admission control threshold if the load control functionhas identified an inadequate admission control threshold for the cell.11. The method according to claim 8, wherein the step of comparingcomprises the substeps of: comparing the received rate of a first TTIand the received rate of a second consecutive TTI with the expectedrate; determining if the received rate of the second TTI is zero, andstoring an indication of insufficient coverage and/or the received rateonly if the received rate of both the first and second TTI are below theexpected rate and the rate of the second TTI is nonzero, wherebydiscerning between low received rate due an ending transmission and lowreceived rate possibly due to poor coverage.
 12. A radio networkcontroller adapted for use in a wireless communication system, thewireless communication system possibly exhibiting load dependent cellcoverage, characterized by: rate measuring means adapted to determine areceived rate from at least one mobile terminal being in a communicationsession, said measuring means arranged to measure the number of receivedtransport blocks during a predetermined time interval; comparing meansin connection with the rate measuring means, and adapted to compare thereceived rate with a predetermined expected rate; and storing means inconnection with the comparing means, and adapted to store an indicationof insufficient coverage and/or the received rate, if the comparingmeans has found the received rate to be below the expected rate.
 13. Theradio network controller according to claim 12, the radio networkcontroller utilizing admission control, further provided with loadcontrol means in connection with the storing means, and adapted tocompare the number of indications of insufficient coverage, or a ratioof transmission giving rise to indications of insufficient coveragecompared to the total number of transmissions, with a predetermined loadvalue and output a suggestion of a lowering of the admission controlthreshold if the number of indications of insufficient coverage, or aratio of transmission giving rise to indications of insufficientcoverage compared to the total number of transmissions is below thepredetermined load value.
 14. A system comprising of a radio networkcontroller and an operation and a management node adapted for use in awireless communication system, the wireless communication systempossibly exhibiting load dependent cell coverage, characterized by: ratemeasuring means adapted to determine a received rate from at least onemobile terminal being in a communication session, said measuring meansarranged to measure the number of received transport blocks during apredetermined time interval; comparing means in connection with the ratemeasuring means, and adapted to compare the received rate with apredetermined expected rate; and storing means in connection with thecomparing means, and adapted to store an indication of insufficientcoverage and/or the received rate, if the comparing means has found thereceived rate to be below the expected rate, and the operation andmanagement node is provided with analyzing means adapted to retrieve thestored indications of insufficient coverage and/or the received ratesfrom the storing means of the radio network controller and identifycells with poor coverage by comparing the number of indications ofinsufficient coverage with the total number of transmissions.